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The secret behind excitation-dependent/-independent photoluminescence of carbon nanodots (CDs) is not yet revealed completely. To address this issue, a detailed investigation on solvent polarity-dependent optical properties of citric acid–urea co-derived nitrogen-doped carbon nanodots (NCDs) was carried out. The interpretation on UV–visible spectral data reveals the presence of H-aggregates formed through hydrogen bonding. In addition, dipole–dipole interaction-mediated J-aggregates are clearly evident. The broad and intense excitation band of NCDs is mostly contributed by highly emissive J-like self-assembly of H-aggregates in polar solvents. Time-resolved fluorescence spectra of NCDs show triexponential decay kinetics. The three lifetime components correspond to long-lived H-aggregates, short-lived J-aggregates, and JH-aggregates of intermediate lifetime. Moreover, fluorescence of NCD is influenced by concentration and storage time. Accordingly, mismatch in spectral shapes of excitation and absorption spectra of NCD can be successfully correlated to aggregate species of NCDs that exist even in very dilute solutions.

Malware detection is a crucial aspect of software security. A malware detector is a system that attempts to determine whether a program has malicious intent. Current malware detectors work by checking for signatures, which attempt to capture the syntactic characteristics of the machine level byte sequence of the malware. This syntactic approach makes current detectors vulnerable to code obfuscations, increasingly used by malware writers that alter the syntactic properties of the malware byte sequence without significantly affecting their execution behavior. This paper derives from the idea that the key to malware identification lies in their syntactic as well as semantic features. It explains an approach using control flow graphs (CFG) for malware detectors . We present an architecture for detecting malicious patterns in executables that is resilient to common obfuscation transformations.

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